Build an Instrumentation amplifier that would do a 10uV -> 10mV amplification

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Woofload
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Build an Instrumentation amplifier that would do a 10uV -> 10mV amplification

Post by Woofload » Wed Nov 08, 2017 8:43 am

Hi,everyone!

I'm trying to build an Instrumentation amplifier that would do a 10uV -> 10mV amplification. The motivation is to measure uA currents on a small enough shunt resistor (1-10Ohm).

For a proof of concept, I've built a circuit like the one below with a distinction that I'm powering it with two 9V batteries and am using LM2902N(http://www.kynix.com/uploadfiles/pdf9675/LM2902N.pdf) as the op amps and Rg is somewhat different. It has much less that the required 1000x gain.
Image

However, when measuring the results for different input voltages, the gain seems to vary:

Image

I was expecting it to be constant.

And here are my questions:

What is a reasonable place to look for the causes of the variations?
  • Cheap resistors?
  • Inadequate op amp?
  • Breadboard prototyping?
  • 2x9V batteries as power supply?
  • other?

bclaire
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Re: Build an Instrumentation amplifier that would do a 10uV -> 10mV amplification

Post by bclaire » Wed Nov 08, 2017 11:20 am

Not sure what this has to do with the Orange forum especially with your first post - please explain yourself before I delete/ban....

Gladmarr
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Re: Build an Instrumentation amplifier that would do a 10uV -> 10mV amplification

Post by Gladmarr » Sat Nov 11, 2017 3:14 am

It doesn’t. But for what it’s worth, check to see if you’re hitting your supply rails or the margin from the supply rails your op-amps can hit before they start to clip. You would probably be better off asking about this in an electronics or engineering forum. Maybe All About Circuits....

Sooner
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Re: Build an Instrumentation amplifier that would do a 10uV -> 10mV amplification

Post by Sooner » Sat Nov 11, 2017 3:45 am

Woofload wrote:
Wed Nov 08, 2017 8:43 am
Hi,everyone!
Hi woof. Welcome to the forum! :lol:
Sooner
AD1512 Serial No. 001

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